Friday, June 16, 2017

It's the time of year I love the most, our field season, when my students and I hit the road. We are making a grand loop, heading north along the spine of the Cascades, with stops at Mt. Shasta, Lava Beds, Crater Lake (above), St. Helens, and Mt. Rainier. We'll then head across eastern Washington through the Channeled Scablands, and climb into the northern Rocky Mountains at Glacier National Park. From there we'll head south into Yellowstone and Grand Tetons National Parks, and cross the Basin and Range Province on our way back home. Y'all have my permission to let up on the heat wave by the time we come back (stay cool and safe). Needless to say, postings on Geotripper will probably be sparse, but I'll give it a try if I can (maybe the laundromats have Wi-Fi out there).

Sunday, June 11, 2017

The summit of Mauna Kea in the distance, and the forested lower slopes of Mauna Loa in the foreground

My last entry on the geological drama of Hawai'i concerned the stubbornness of life in a harsh volcanic environment, such as that which is found on the highest slopes of Mauna Loa and Mauna Kea on the Big Island of Hawai'i. I was echoing of course one of the memorable lines from the movie "Jurassic Park". As I started to review my next set of pictures from my recent trip, I realized the opposite supposition also holds true: rock finds a way (to kill life).

Lua Manu Crater on Chain of Craters Road. It formed by collapsing several hundred years ago, and was later filled with lava flows in 1974.

Now obviously, it couldn't be clearer that lava destroys life as it flows through and burns forests. The aftermath of many a flow is a barren plain with no sign of life of any kind. In the tropical climate of Hawai'i, life returns quickly as wind and water aid in the propagation of seeds from the nearby forest. Sometimes it is bird droppings that scatter the seed and provide the first nutrients that lead to a rebirth of life. The surface of the Big Island gets made over repeatedly over the millennia.

The battle between rock and life does take unusual forms sometimes, which is what I wanted to illustrate in today's post. Basaltic lava is not always the all-consuming fiery hell we often take it to be. It may be in excess of 2,000 degrees Fahrenheit (1,100 degrees Celsius) as it flows from the vent, but when the lava encounters cold objects, the surface of the lava can freeze quickly. When the object is a tree, strange things can happen.

On the slopes of Kilauea or Mauna Loa, the most common tree is the Ohi'a, which I wrote of in the previous post. In 1974, the Keanakāko‘i flow overwhelmed an Ohi'a forest near Chain of Craters Road in Hawai'i Volcanoes National Park. The lava froze around the trunks as the trees themselves caught fire and burned away.

The resulting cavities are called tree molds, and they were spread widely in the Keanakāko‘i flow. The charcoal from the former tree can still be seen in some of the molds after forty years (below).

At times, the molds perfectly preserve the pattern of the bark, as can be seen below.

There is another odd phenomena that occurs in these events. The lava flows past the trees, solidifying around the trunk, and continuing on. It's not always obvious, but as lava flows by, the thickness can change, and the level of the flow can drop around the trees. The tree molds are left behind as towers of basalt with hollow centers (lava trees). It's actually kind of eerie to encounter such ghosts in the midst of a living forest (below), and easy to understand how ancient people considered these to be people turned to stone by the gods.

The 1974 has hundreds of these lava trees, and some take bizarre shapes, as in the case below, where a multiple-trunked tree (or a clump of several) was preserved.

It's obvious that life is slowly being reestablished on the flow, as we were surrounded by Ohi'a trees and other species at various stages of growth.

It turns out that the tree molds themselves offer a hospitable environment for life, with nutrients provided by the charcoal, and cooler wetter conditions below the surface.

The lava forests can be seen in several places. By far the easiest is at Lava Tree State Monument in the Pahoa area. It resulted from a flow in 1790, and the park offers paved accessible trails and interpretive signs. If you want to see the Keanakāko‘i ghost forest, you'll find it in the vicinity of Lua Manu Crater on Chain of Craters Road in Hawai'i Volcanoes National Park. There are no signs and no trails, so you are in for a bit more of a rugged adventure. Be prepared with water, sturdy shoes, and the other usual things you need for a wilderness outing. And...be careful while studying the ghost trees. Many are unstable and fragile and could be destroyed by a thoughtless climb or push. And having one fall on you can't possibly end well.

Tuolumne River on Feb. 21, 2017, discharge about 16,000 cubic feet per second

There is no doubt that this has been a unique year for the rivers of California, one that could very well not be repeated in many of our lifetimes. A year ago we were in the grips of the worst drought ever recorded, five years running, and then the rains began. And continued. Month after month, one atmospheric river storm after another took aim at California like an out-of-control fire hose. The snowpack reached levels not seen in generations, in some places reaching 200% of normal.

Tuolumne River this afternoon, discharge 3,520 cubic feet per second

And then things got scary. Oroville Dam came uncomfortably close to failure, requiring the evacuation of 200,000 people downstream for a period of time. Don Pedro Dam on the Tuolumne River was not in danger of failure but it came within inches of overflowing uncontrollably, and the emergency floodgates were opened for only the second time in history (the first being in 1997). On January 4, operators at the dam ramped up flows of the river to 10,000-12,000 cubic feet per second (for a day or two, flows reached 16,000 cfs), putting it in a state of official flooding, and the water flows did not begin to recede until only a few days ago. I checked out the river a week back, and the river was down to 6,000 cfs. Today it was 3,520 cfs, and after five months of constant inundation, the floodplain was at long last reemerging. For perspective's sake, the average flow of the river during much of the drought was around 200-500 cubic feet per second.

On Feb. 21, the river was flowing into the large quarry pond on the top left of the picture.

The snowmelt has not actually slowed down, actually. The inflow into Don Pedro Reservoir has remained constantly above 12,000 cfs for much of the last month, but apparently the dam operators are feeling confidant that they can fill the dam without overflowing, and have allowed the lake level to rise slowly from 798 feet to 815 feet (it would be full at 830 feet). This is the delicate dance they must do to maintain flood protection while preserving as much water in storage as possible for irrigation and domestic use downstream.

Today, the river and the pond are separated again. The floodplain in the foreground is once again exposed.

I've been wondering ever since the floodplain was inundated how the channel of the river would be affected by the ongoing deluge. At such high flow velocity, cobbles and gravel have surely been redistributed across the floodplain. It is not yet clear whether the river will find a new channel, but I would not be surprised if that happens. I can see new sandbars that may be blocking old channels in a few places. I wondered if the slough at the base of the metal stairway on my river trail would become a new channel, but it's looking like it will not, but it may be longer than it once was.

The most apparent change will be in the riparian vegetation. There had been a great deal of growth on the floodplain since the last inundation in 1997, and much of that vegetation has been swept away. Whole mature trees are gone, and entire willow thickets. A bit of good news in that regard is the complete absence of river hyacinth. The invasive plant was well established on the upper Tuolumne, but all sign of it has been swept away in the torrent. I hope the same has happened downstream at the confluence with the San Joaquin and in the delta. The hyacinth has choked channels and blocked out native plants and wildlife. Maybe this event will be a reset, and some form of control can be achieved.

The other changes to consider are the animals. The floodplain was a rich habitat for all manner of mammals, reptiles, amphibians, fish, and creepy crawlers. Many have been displaced for months, and their former homes will be highly altered or gone. There will be large tracts of barren gravel. I'll be watching for their return.

The floodplain of the Tuolumne was not a natural river before the flood. Gold mining, dredging, and quarrying had already severely damaged the riparian environment, and altered the natural channel. There were few of the gravel bars needed by the salmon and other native fishes to spawn. I am hopeful that the flood will have made some positive changes.

The deluge is not yet over. There is still a huge amount of snow in the high country, and flows will no doubt remain high for weeks or months to come. The full extent of the changes to the floodplain will not be apparent for some time. I'll be there to report when they are!

Friday, June 9, 2017

Ohi'a Lehua (Metrosideros polymorpha) clinging to a crack in a 1974 lava flow on Kilauea

I had kind of a schizophrenic (split-brain) response in regards to what I wanted to accomplish with this post. A couple of weeks ago while still in Hawai'i, I did a post on what I considered the ultimate wilderness on planet Earth, the nearly lifeless high-altitude basalt flows of Mauna Loa on the Big Island. At first, as a follow-up, I was thinking of the idea of how life finds a way to propagate even in the most barren settings. As I went along though, I started to think about how rock is destroyed, and how often life has something to do with the destruction. Whatever way this post decides to go, the unique Hawaiian tree Ohi'a Lehua (Metrosideros polymorpha) is going to have something to do with it.

The Ohi'a is one of the most remarkable tree species on the planet. The Latin name polymorpha ('many shapes') provides a clue why: it can grow in a stunning number of deeply contrasting environments. Ohi'a trees can be found as the first pioneering species on fresh lava flows, as in the pictures above. They can be found on the near-desert leeward slopes of the island's volcanoes. They form the canopy of most of the island's rainforests, growing to heights approaching 100 feet (30 meters). They grow in near alpine conditions at 8,000-9,000 feet on Mauna Loa and Mauna Kea. And stunted trees, barely shrubs, survive in the high altitude bogs on Kauai where the rainfall exceeds 300 inches a year. I know of no other tree species that is capable of such feats.

It's true that you could try and cultivate Ohi'a trees in these kinds of environments elsewhere in the world and they might not do very well in competition with other established species. On Hawai'i, though, all they have to do is survive, because the isolation of the islands has meant that only a handful of other tree species ever arrived. So it is that in the unending battle between rock and life in Hawai'i, the Ohi'a tree is often the main combatant.

The Ohi'a trees aren't entirely alone as colonizers of barren landscapes in Hawai'i. The ʻŌhelo ʻai (Vaccinium reticulatum) is a shrub that can be found on new cinder cones, ash fields, lava flows and alpine slopes. The berry is edible, and is a treat for the nēnē, the native Hawaiian Goose. The geese in fact have a lot to do with spreading the seeds in the inhospitable environments of volcanic landscapes (they leave the seeds in their droppings). I'm trying to think of any other plant or shrub that produces mature fruit when it is only an inch or two high (as in the picture below).

ʻŌhelo ʻai (Vaccinium reticulatum)

There are a number of native fern species as well, growing in the most inhospitable environments I can imagine. Those below are growing in a pit on the flank of Mauna Ulu, which came into existence during a series of eruptions from 1969 to 1974.

And then there were the "furry rocks" I saw on Saddle Road at the pass between Mauna Loa and Mauna Kea. The mosses and lichens survive on the surface of the rock itself, and draw out nutrients directly from the minerals. The acids produced by the plants contribute to the alteration of the basalt to various clay minerals that end up producing pockets of soil that support numerous other plants. Forest succession eventually produces mature rainforests over time (at least with the cessation of constant lava flows as some of the volcanoes go dormant).

I guess "life finds a way" ended up as the predominate theme as I wrote. I was musing, though, about those high slopes of Mauna Loa at 11,000 feet where I saw no visible life. All the normal ways that rock is destroyed don't seem to apply up there. There are no plants to aid in the production of soil. There are no rivers to carry away sediment (any water seeps into the cracks and fractures of the lava flows and emerges far downslope). There are no glaciers. Snow falls on both Mauna Loa and Mauna Kea, and there were glaciers thousands of years ago, but they have little influence in the present day (one of the talks at the conference I attended concerned the permafrost at the summit of Mauna Kea). Waves can't attack the rocks until the islands have subsided enough, a process taking millions of years. Mass wasting has little effect on the gentle slopes of the giant shields, although gigantic megaslides eventually destroy the flanks of the volcanoes and ultimately lead to their destruction. The barren lava fields on the high flanks of Mauna Loa seem permanent until one realizes that they will no doubt be covered by new lava flows in a matter of decades or centuries. And when the volcano goes dormant or extinct, time (and life) will indeed destroy the rocks.

Sunday, June 4, 2017

Crystal Springs Reservoir is on the upper left, while San Andreas Reservoir is on the lower right

As has been no doubt obvious, I was in Hawai'i last week, and there have already been several posts about some of my adventures. I started through the many pictures in a more chronological manner, and realized there were some neat things I saw before I even left California. I always notice on a flight that some people do such things all the time and are not particularly impressed that they are in a large metal tube traveling at hundreds of miles an hour at 35,000 feet. Others have a sense of history, realizing that for the first few million years of hominid existence, this was an unnatural thing to be doing. I don't get to fly all that often, so I tend to fall into that second category. As soon as we are off the ground, the camera that I surreptitiously placed at my feet swings into place and I start snapping pictures as if I were the first human being ever to see such incredible sights. My photo habit led to my first blog series in 2008, the Airliner Chronicles. Consider this a new entry...

It is the geologist's perspective that provides some insight as to the nature of the landscape below. We left from Oakland Airport and flew over the north end of the San Francisco Peninsula, which provided an outstanding view of the San Andreas fault. Often such faults are indicated by linear valleys owing to the ease with which crushed rock in the fault zone erodes. But on the peninsula the fault is even easier to pick out because of the presence of two reservoirs filling the linear valley, Crystal Springs reservoir, and San Andreas reservoir.

It's quite a coincidence, the fault and the lake both being called "San Andreas", so the question naturally arises, which was named first? The fault may be more famous to most people, but the lake came first. It was constructed in 1868. In 1895, the geologist Andrew Lawson was mapping in the area and discovered the fault, which he named after the lake. He had no idea that the fault was 600 miles long, or that it was particularly active, or that it was the boundary between the Pacific and North American tectonic plates. And he most certainly didn't know that it would shift in 1906 in a most tragic way.

The city has grown in the years since 1906, to say the least. We know a great deal more about fault zones and earthquakes, and thus we have a better understanding about the threats of future quakes in the Bay Area. Both by law and by subsequent experience (Loma Prieta in 1989 and the Napa Valley in 2014), the cities of the peninsula are better prepared for large earthquakes, but no matter how ready they may be, the next large earthquake will cause major damage on the peninsula and many will die or be injured. Seeing the proximity of the fault and the cities from above provides a stark reminder of the need to be prepared.

We flew out over Half Moon Bay, and soon land was left behind. There was more than 2,000 miles of open ocean ahead of us, a five hour flight. I settled in and thought of how the islands were inaccessible to humans of any kind until only a thousand or so years ago, and even a hundred years ago it took weeks or months to cross the ocean. How even more wondrous the number of bird and insect species that survived the journey over the millennia.

Friday, June 2, 2017

If you've had a geology or earth science course, do you remember what you learned about basalt? Basalt, the low-silica volcanic rock, the one that flows instead of exploding. The one that isn't all that dangerous. Even if you haven't had such a class, you've heard that visiting volcanoes on the Hawaiian Islands is one of the things tourists can do. Helicopters fly over the lava flows, and people watch lava pouring into the sea from a few hundred yards (or feet) away. Basalt is the black volcanic rock with holes in it.

Pele's Hair collected near the edge of Kilauea Caldera

In my last post, I provided a bit of a mystery, a series of circles found in the barren plains near the summit of the Kilauea caldera on the Big Island. I'm going to provide the answer (and yes, someone accurately solved it), but first I'd like to show you some unusual things you'll see if you get access to some parts of the Kilauea volcano complex.

First off, the stuff in the first two pictures. These fibers are found around the summit area of Kilauea, and in protected hollows they can accumulate in large masses. It's called Pele's Hair, and it's made of natural volcanic glass, otherwise known as obsidian. Glass is not usually associated with basalt in the minds of most people, but glass can form around any lava that cools so quickly that crystals can't readily form. This odd feature develops around spattering edges of lava lakes like that which currently resides in the crater of Halemaumau. As globs of liquid are thrown into the air, some of the liquid trails behind as a thin fiber, which then breaks off and floats away in the turbulent hot air currents. If you visit the Big Island, you can usually find some near the Jagger Museum on the crater rim.

Reticulite from Kilauea Caldera

Then there is this weird material that can also be found around the summit region of Kilauea. It made me think of old weathered sponge rubber, but it is no such thing. It is a rock. It's composed of volcanic glass, and could be described as a sort of golden pumice, but it is distinctly different from any pumice I've ever seen. It's lighter, for one thing, and that is hard to believe, even while holding it in your hand. Most pumice is between 64-94% air bubbles, but this material exceeds 95% air. The walls of the bubbles are so thin that many are open, and this rock will not float the way that pumice can because it fills with water too quickly. It is called reticulite. It's so light that it can be blown a long ways from a crater by high winds. It is so delicate it can be crushed between one's fingers, and it can't be expected to last long in most geological environments.

Close up of reticulite from Kilauea

And finally there is this rock outcrop on the rim of Kilauea Caldera. It looks, well, almost like sedimentary layers! That is most decidedly not the kind of thing one expects to find on the edge of a basaltic shield volcano, the edifice that is supposedly constructed by multitudes of basaltic lava flows. What the heck is going on here, and what does it have to do with the strange circles of our little mystery?

A closer look reveals that these are layers of volcanic ash and scoria, the smaller particles that are associated with explosive eruptions, the kind we expect to find on the slopes of a Mt. St. Helens or a Mt. Shasta, the stratovolcanoes found on continental landmasses near subduction zones. What was going on here? The layers are more than 30 feet thick, and have been named the Keanakāko‘i Tephra.

Keanakāko‘i Tephra partially covered by a 1983 basalt flow.

It's clear that what we get taught about basaltic lava is not the entire story. Sometimes basalt erupts violently, and as such it can be exceedingly dangerous. An eruption in 1790 killed several hundred Hawaiian warriors on the eve of a major battle, and the event changed Hawaiian history, as the tragedy was seen as the judgment of the gods. These deposits were once thought to be the results of the 1790 eruption, but it turns out that they include dozens of explosive eruptions that took place between about 1500 and the early 1800s.

Exposures of the Keanakāko‘i Tephra on the margin of the Kilauea Caldera. A 1983 basalt flow can be seen below on the right.

What caused this explosive activity? In a word: water. When rising magma encounters groundwater, the water can flash to steam, causing intense explosions. Apparently the caldera collapsed to a depth great enough to reach the regional water table, and huge explosions ensued. Something like this happened at Kilauea in 1924 (see the picture below), but the massive explosions totaled only about 1% the volume of the 1790 and earlier eruptions. There have been some seriously dangerous eruptions throughout time on this volcano.

And that brings us to the strange circles of the mystery. In 1924 some huge blocks were thrown out of Halemaumau crater and were thrown a thousand or more meters. When they landed, they produced bowl-shaped craters. One of the biggest from 1924 weighed 8 tons, and can be seen in the picture below.

Subsequent eruptions produced Pele's Hair, reticulite, and small cinders or coarse ash. All of these particles blew across the landscape, and accumulated in the shallow craters. The blocks remain visible in the centers of some of the craters, while others are buried. The filled craters in some cases trap water more efficiently than other surfaces, so plants are able to gain a foothold (roothold?) in the craters.

The evidence of 300+ years of explosive eruptive activity around Kilauea is sobering. Such eruptions have the potential to do serious damage to surrounding communities around the caldera and in the Puna District to the east. Current research is seeking to better understand the cycle of activity surrounding these periods of violence.

It was a real privilege to explore the flanks of Kilauea Caldera with Don Swanson, Tina Neal, and Frank Trusdell of the Hawai'i Volcano Observatory during my visit to the islands last week. It was a fascinating learning adventure. More stories to come!

About Me

I am a teacher of geology at Modesto Junior College and former president of the National Association of Geoscience Teachers, Far Western Section. I have led field trips all over the western United States, and a few excursions overseas, but my homebase is the Sierra Nevada, the Great Valley, and the Coast Ranges of California.

Ask Geotripper

Is there something about geology that you are curious about? Do you have questions about the scientific aspects of political controversies? I can try to provide a scientist's perspective. Your questions and possible answers could be a springboard to a blog discussion, or they can be private. Anonymity is always assumed. Contact Geotripper at hayesg (at) mjc.edu.

Blooks, Boogers and Bleries

Here are some of the series I've produced for the Geotripper Blog:

The Other California: what to see when you've seen all the really famous places in the Golden State (in progress).Into the Great Unknown: A rafting journey down the Colorado River through the Grand Canyon. The most incredible adventure of my life (so far)!

The Hawai'i That Was: An exploration of the geology, natural history, and anthropology of the most isolated lands on the planet. It's a lot more than beaches, shopping, and palm trees!